Phytoplankton Taxonomic Composition Research Articles

Water quality and habitat drive phytoplankton taxonomic and functional group patterns in the Yangtze River

BackgroundAlthough phytoplankton are important primary producers in food webs, they are relatively less studied in large rivers compared to other types of systems. To fill this research gap, we studied phytoplankton taxonomic and functional composition and their relationships with water quality, habitat, climate, and land use across 30 river sections in the middle and lower reaches of the Yangtze River during 2017–2018.ResultsMajor observed phytoplankton groups were cyanobacteria, bacillariophyta, and chlorophyta. Phytoplankton total abundance, total biomass, and species richness significantly decreased in the dry season compared to the wet season, with the species and functional composition differing significantly between seasons. Phytoplankton species differences between seasons were mainly contributed by Oscillatoria sp., Pseudanabaena sp., and Melosira granulata. The dfferences in phytoplankton functional groups between seasons were mainly contributed by P (including Closterium sp., Melosira sp.), Lo (including Merismopedia sp., Peridinium sp., Ceratium sp., and Gymnodinium sp.), and J (including Pediastrum sp., Tetraedron sp., Crucigenia sp., Scenedesmus sp., and Coelastrum sp.). The variance partitioning showed that water quality (NO3-N, total suspended solids, turbidity) and habitat (water flow, river bank and river channel conditions) were critical factors in shaping phytoplankton patterns, followed by climate and land use.ConclusionsResults indicated that there was significant seasonal variation of phytoplankton in the Yangtze River, with water quality and habitat primarily driving phytoplankton patterns. Our study contributes to the understanding of natural and anthropogenic factors that drive seasonal successional processes of phytoplankton in the Yangtze River. These findings have important implications for environmental management as well as towards the ecological restoration of large rivers.

Taxonomic composition and abundance of phytoplankton in the floodplain reservoirs of the Upper Ob (near the city of Barnaul)

The data on taxonomic composition of phytoplankton in floodplain reservoirs of various types (chute, oxbow and oxbow lake) of the Upper Ob served as an subject of the present study. The total taxonomic diversity amounted to 78 taxa (genus definition) belonging to 7 divisions: Bacillariophyta - 24 genera, Chlorophyta - 27, Ochrophyta - 11, Cyanobacteria - 8, Dinophyta - 4, Euglenophyta - 3 and Cryptophyta - 1 genus. Diatoms dominate in the number of taxa in the chute presented by the Bacillariophyta division; in oxbow and oxbow lake representatives of the greens, division Chlorophyta. There is the highest frequency of occurrence of large taxa: in the chute - diatoms 83.3 % and green - about 58.3 %; in the oxbow - single-celled golden - 91.9 %, green - 82.0 % and diatoms - 72.7 %; in the oxbow lake - golden -82.0 % and diatoms - 54.5 %. The maximum phytoplankton biomass values were detected in the lake in spring at the end of April - 4551.6 mg/m3, while in the chute the maximum for this indicator was reached only in mid-June - 673.1 mg m3. For the oxbow, the top of phytoplankton biomass was noted in early June - 1947.8 mg/m3 and in the end of July - 1807.0 mg m3. According to the biomass level of phytoplankton, lake and oxbow belong to mesotrophic reservoirs (up to 1.0 - 5.0 g/m3), the chute - oligotrophic (up to 1.0 g/m3).

СОСТОЯНИЕ ПЛАНКТОННЫХ СООБЩЕСТВ НИКОЛЬСКОГО УСТЬЯ РЕКИ СЕВЕРНАЯ ДВИНА В ОСЕННИЙ ПЕРИОД 2022 ГОДА

The work is part of the environmental monitoring of the Nikolskaya estuary. Severnaya Dvina, carried out in 2022, with the aim of comprehensive research of aquatic biological resources and their environment. Information was obtained on the species diversity and structure of plankton communities of the studied object belonging to the drainage basin of the Severnaya Dvina River. The taxonomic composition of phytoplankton and zooplankton in the navigation period of 2022 is shown. Species diversity was assessed using the Shannon index, based on the relative abundance of species, the Menhinik, index, which determines species richness, the average abundance and biomass of phytoplankton of the Nikolsky Estuary were determined. The Pantle-Bukka saprobity index was calculated to assess the pollution of natural waters. According to observations, 53 algae taxa with a rank below the genus and 21 zooplankton organisms have been registered. It was found that the basis of algoflora was diatoms. Copepoda copepods formed the basis of the zooplankton community. New data on the state of phytoplankton and zooplankton communities can serve as an informational and methodological basis for the development of environmental monitoring programs for aquatic ecosystems in the region.

Human activity as a factor causing the biomass, structure and seasonal dynamics of phytoplankton in adjacent fishponds

The role of phytoplankton as one of the main sources of energy entering the water food network is especially evident in fish-rearing ponds. Indeed, in these comparatively small ponds (unlike many lakes), variations in the abundance of phytoplankton can be extremely sensitive to the action of external factors, including human activity. Here, we present results of the analysis of the phytoplankton dynamics in adjacent fishponds and in supplying/recipient river courses upstream and downstream of the ponds during a growing season. In the grow-out ponds, phytoplankton biomass is shown to reach maximums in spring and in early autumn, while in the nursery pond, the phytoplankton dynamics is characterized by one long peak. The specificity of fish-rearing ponds as the human-regulated reservoirs clearly manifests itself under comparison of phytoplankton biomass of ponds with the biomass of phytoplankton inhabiting a nearby river. The averaged phytoplankton biomass in the ponds was 6.2–10.1 times higher than in the river. Besides, we show here that the taxonomic composition of phytoplankton in the river differs significantly from the composition of phytoplankton in the fish-rearing ponds. In particular, Cyanobacteria and Chlorophyta were revealed as the major portion of the phytoplankton in the fish-rearing ponds, while in the river their abundances were low.

Structural and functional characteristics of phytoplankton, algal mats, detritus and water quality under main abiotic factors in urban ponds (case study of urban settlement Hostomel, Bucha district, Kyiv Region, Ukraine). Report І. Species and taxonomic composition, ecological diversity of phytoplankton and filamentous algal mats characteristics under main abiotic factors

The paper considers species and taxonomic composition of phytoplankton and algal mats in ponds of Hostomel urban settlement under effect of main abiotic factors. The research was carried out in May 2021. The ponds under study are shallow and the photic zone occupies the entire water column. The dissolved oxygen content was high. According to nutrient content the ponds are eutrophic. Planktonic algal communities were marked by high diversity. The identified algae referred to 8 phyla, 13 classes, 29 orders, 49 families, 87 genera and 134 species, represented by 136 infraspecific taxa. The floristic diversity at the phylum level was mainly formed by Chlorophyta, Bacillariophyta and Cyanobacteria, at the class level – Chlorophyceae, Bacillariophyceae and Cyanophyceae, at the order level – Sphaeropleales, Euglenida, Chloreallales and Bacillariales, at the family level – Scenedesmaceae, Euglenidae, Bacillariaceae, Selenastraceae and Chlorellaceae, at the genus level – Desmodesmus, Nitzchia, Monoraphidium, Trachelomonas and Euglena. According to biotopic preference planktonic and planktonic-benthic forms prevailed. In Pond ІІІ, floating algal mats were observed. They appeared when benthic communities composed of Charophyta, Bacillariophyta, Chlorophyta and Euglenozoa rose to the water surface. Their cell count reached 28168–368149 thousand cells∙m–2, biomass – 21–362 g ∙ m–2. Algal mats caused a local negative effect due to water column shadowing. High diversity of algal communities makes it possible for pond ecosystems to function even under human impact.

Impact of the Construction of New Port Facilities on the Biomass and Species Composition of Phytoplankton in the Neva Estuary (Baltic Sea)

The construction of new port facilities and the creation of new lands is a natural consequence of the rapid growth in the population of ocean coastlines. Despite the fact that such human activity is becoming more and more widespread, its impact on various components of aquatic ecosystems, including phytoplankton, is still poorly understood. The aim of the study was to assess the effect of the large-scale construction of new port facilities on biomass and taxonomic composition of phytoplankton in the Neva Estuary (northeastern Baltic Sea). Studies have shown that digging and displacing large amounts of bottom sediments during these works led to a significant increase in suspended mineral matter and a decrease in water transparency in the estuary. This significantly reduced the species richness and biomass of phytoplankton. However, the analysis of beta diversity did not show significant changes in the phytoplankton community during the periods of port construction and the periods when no works were carried out. The changes mainly concerned rare species, while the occurrence and biomass of dominant and subdominant species changed to a lesser extent. Due to various adaptations, the phytoplankton species common in the estuary are apparently able to survive under prolonged shading and successfully compete with species that are unable to withstand the lack of light for a long time. To correctly take into account the effects of the construction of new port facilities on phytoplankton and, if possible, minimize it, additional studies of the ecology of certain phytoplankton species, their relationships, and physiological responses to various environmental factors are required.

Phytoplankton and seston fatty acid dynamics in the northern Bering-Chukchi Sea region

Arctic and subarctic ecosystems are transitioning due to ocean warming, resulting in conditions that will lead to shifts in phytoplankton communities, their nutritional compositions, and production of fatty acids (FAs). FA biomarkers are useful indicators of changing phytoplankton community composition and provide insight into basal resource quality for higher trophic level consumers such as zooplankton, fish, birds and marine mammals, yet phytoplankton FA information is largely lacking from the Bering and Chukchi Sea regions. Therefore, we analyzed suspended particulate matter (seston) FAs, chlorophyll-a (Chl-a) and environmental data collected from four surveys in the northern Bering and Chukchi Seas, two during June of 2017 and 2018 and two during August and September 2017 and 2019. Our objectives were to determine 1) whether seston FA composition was correlated with phytoplankton taxonomic composition analyzed using imaging microscope (FlowCAM) techniques, 2) if there were seasonal differences in seston FA concentrations, and 3) how FA concentrations varied with environmental variables. We found significant seasonal differences in seston FA compositions, with diatom biomarkers more prevalent in spring, followed by a community shift to dinoflagellate and small flagellate FA biomarkers in late summer. These results were confirmed by FlowCAM analyses. FA biomarkers were correlated with total and large size-fractioned Chl-a concentrations, nitrogen concentration and temperature. Lastly, we used a model framework to predict availability of the diatom-associated essential FA, eicosapentaenoic acid (EPA, 20:5n-3). Our analysis provides new information on phytoplankton FA dynamics and the important nutritional role of phytoplankton for higher trophic level consumers in the northern Bering and Chukchi Sea regions.

Seasonal influence of intrusion from the Kuroshio Current on microplankton biomass and community structure in the northern Satsunan area, western Japan

Seasonal variations in hydrographic conditions, nutrients, and microplankton abundance and biomass were investigated inside and outside Kagoshima Bay in the northern Satsunan area. The area is a nursery ground for the migrating fish. During the mixing season from November to April, highly saline water (>34.5) originating from a branch of the Kuroshio Current, the western boundary current of the North Pacific Subtropical Gyre, intruded from the surface layer into the bay causing extrusion of coastal bottom water. This intrusion generated vertical mixing between surface water and nutrient-rich bottom water. Consequently, chlorophyll a concentrations increased (>1 μg l−1) around the bay mouth. During the stratified season from May to August, the coastal surface water was extruded due to intrusion of saline water from the bottom layer. High chlorophyll a concentrations (>1 μg l−1) were also observed in the surface layer in July during the rainy season. Such differences in hydrographic conditions between mixing and stratified seasons were due to vertical distribution of highly saline water from outside the bay, which seasonally migrated between surface and subsurface layers. Relatively distinct redundancy analysis plots and boxplots generated from a generalized linear model showed that microplankton community structure differed between mixing and stratified seasons. The mixing and stratified seasons were characterized by high diatom abundance and low microplankton abundance, respectively, suggesting that vertical mixing increases nutrient supply and consequently increases diatom abundance. Thus, microzooplankton (mainly naked ciliates and athecate dinoflagellates) abundance was related to the abundance of prey organisms, such as diatoms, thecate dinoflagellates and cryptophyte-like flagellates, rather than hydrographic conditions. Thus, saline water intrusion from a branch of the Kuroshio Current likely governs hydrographic conditions in Kagoshima Bay and consequently affects temporal variations in abundance and taxonomic composition of phytoplankton and microzooplankton communities.

СОВРЕМЕННОЕ СОСТОЯНИЕ ПЛАНКТОННЫХ СООБЩЕСТВ НИЖНЕГО ТЕЧЕНИЯ РЕКИ ВЫЧЕГДА И ЕЕ ПРИТОКОВ

The work is a part of the comprehensive studies of the rivers and lakes of the south-east of the Arkhangelsk region, carried out in 2021 for the purpose of development of aquaculture of inland water bodies. The data on the species diversity and structure of plankton communities of freshwater bodies belonging to the Vychegda River watershed were obtained. Taxonomic composition of phytoplankton in summer period of 2021 was shown. Species diversity was estimated using Shannon index based on relative abundance of species, Menchinic index to determine species abundance, and Jaccard's similarity coefficient. Pantle-Bucca saprobicity index was calculated to assess pollution of natural waters. Evaluation of watercourses trophicity based on the obtained indicators of phytoplankton and zooplankton was carried out. We have identified 192 taxa of microalgae from 8 divisions and 15 species of zooplankton from three systematic groups. Green and diatom algae were found to be the basis of the algoflora. The zooplankton community was cladoceric-copepodic. New data on the state of the phytoplankton community can serve as an informational and methodological basis for the development of ecological monitoring programs for the aquatic ecosystems of the region. The results of the research can be used to assess the fish productivity of the Arkhangelsk region water bodies and to calculate the damage to aquatic bioresources from economic activities.

Variability of hydrographic factors, biomass and structure of the phytoplankton community at the entrance to the Gulf of California (spring 2013)

This study reports observations of the horizontal and vertical variation of chlorophyll a (Chla) and the taxonomic composition of phytoplankton at the entrance to the Gulf of California (GC) and its relationship with physicochemical processes. This region is part of the northern boundary of one of the largest shallow Oxygen Minimum Zones in the world, characterized by marked physicochemical gradients. Therefore, understanding the prevailing seasonal patterns and their relationship with primary producers is considered particularly relevant. The study period, April 2013, was characterized by mesoscale eddies and fronts associated with several water masses (California Current Water - CCW, Gulf of California Water - GCW, and Subtropical Subsurface Water - StSsW), which influenced the horizontal and vertical distribution of Chla between 0 and 150 m. Superficial southward flow of CCW was observed near the west coast of Baja California, turning toward the GC flowing between 30 and 60 m depth. At the entrance to the GC, the currents circulated anticyclonically, flowing into the GC near Baja California, while GCW flowed out of the GC near the mainland coast. The vertical distribution of Chla featured a subsurface maximum layer (SCML) associated with the 25 kg m-3 isopycnal, highlighting the importance of stratification processes as drivers of the vertical distribution of phytoplankton biomass. In turn, this favored different associations of phytoplankton groups. In surface waters, the phytoplankton community was dominated by picocyanobacteria (Synechococcus and Prochlorococcus) and Prymnesiophytes, while at the SCML, Prymnesiophytes coexist mainly with Prasinophytes, Chrysophytes, and Cryptophytes. The prevalence of these flagellates (and the absence of autotrophic dinoflagellates) suggests the importance of a multivorous food web in this region, typical of environments where carbon recycling predominates in the pelagic zone. Diatoms made no significant contribution to Chla, although their abundance increased in the SCML associated with the influence of the CCW. The low N:P (8.3) and Si:N (0.86) ratios indicate that nitrates and silica are potentially limiting nutrients for the development of this group.

Biochemical Composition of Seston Reflecting the Physiological Status and Community Composition of Phytoplankton in a Temperate Coastal Embayment of Korea

The biochemical composition of seston along a salinity gradient were examined in the low-turbidity, temperate, estuarine embayment, Gwangyang Bay in Korea. Seasonal variations in sestonic protein (PRT), carbohydrate (CHO), and lipid (LIP) concentrations were analyzed to assess the effects of physiological status and taxonomic composition of phytoplankton. The concentrations of biochemical compounds displayed a close relationship with chlorophyll a (Chla). PRT:CHO ratios were high (>1.0) in the estuarine channel in warmer months and in whole bay in February, indicating a N-replete condition for phytoplankton growth. High CHO:LIP ratios (>2.5) in the saline deep-bay area during the warmer months (>2.0) emphasized the importance of temperature and photoperiod over nutritional conditions. The low POC:Chla (<200), molar C:N (~7) ratios, and biopolymeric carbon concentrations coupled with high primary productivity indicated a low detrital contribution to the particulate organic matter pool. Diatom dominance throughout the year contributed to consistently high carbohydrate concentrations. Furthermore, generalized additive models highlighted that phytoplankton community (i.e., size) structure may serve as an important descriptor of sestonic biochemical composition. Collectively, our results suggest that physiological and taxonomic features of phytoplankton play prominent roles in determining the biochemical composition of seston, supporting the fact that the ecosystem processes in Gwangyang Bay are largely based on phytoplankton dynamics.

Diversity and Abundance of Phytoplankton in the Coastal Waters of South Sulawesi

Phytoplankton are primary producers that can be used as seawater condition indicators. Certain phytoplankton can proliferate, causing harmful algal blooms (HABs). The coastal waters of South Sulawesi, Indonesia are under pressure from land-based processes and activities resulting in inputs of organic and inorganic materials. This study analysed phytoplankton diversity and abundance in coastal waters around South Sulawesi. Phytoplankton were sampled and seawater parameters (salinity, temperature, turbidity, pH, nitrate concentration) measured in-situ at six stations around seven major river estuaries in three seaways (Makassar Strait, Flores Sea, Gulf of Bone). Phytoplankton taxonomic composition, abundance and indices of diversity (H’), evenness (E), and dominance (D) were analysed. Phytoplankton from 31 species and three classes (Bacillariophyceae, Cyanophyceae, Dinophyceae) were identified. Phytoplankton abundance and community structure differed significantly between sites and seaways but were not significantly correlated with water quality parameters although Dinophyceae abundance correlated significantly with observed pollution levels. Phytoplankton abundance was strongly influenced by the Dinophyceae, especially Ceratium furca, a potential HAB species; Cyanophyceae had the strongest influence on species richness but least on community structure. C. furca abundance was strongly correlated negatively with species richness, H’ and E, and positively with D, indicating negative impacts of this species on phytoplankton communities.

Phytoplankton responses to solar UVR and its combination with nutrient enrichment in a plateau oligotrophic Lake Fuxian: a mesocosm experiment.

Multiple stressors associated with global change are influencing the phytoplankton taxonomic composition and biomass in plateau lakes, such as higher levels of ultraviolet radiation (UVR, 280-400nm) and the risk of eutrophication. Although the restrictive effects of high UVR on phytoplankton are generally recognized, the effects will be impacted by the UVR levels of seasonal changes and the nutrient status. In this study, in situ phytoplankton productivity was measured seasonally under full solar radiationand only visible light (photosynthetically active radiation, PAR) conditionsin the plateau oligotrophic Lake Fuxian, Southwest China. To determine the single effects of UVR and nutrient enrichment and their combined impact on phytoplankton communities, a mesocosm experiment (1month) was conducted outdoors during late summer (rainy season). The interactive experiment was designed with two radiation treatments (UVR + PAR and PAR) and four nutrient treatments (raw water, nitrogen addition, phosphorus addition, nitrogen and phosphorus addition). Our results suggested that the response of phytoplankton to UVR depended largely on nutrient availability, which was embodied in the no significant responses of phytoplankton productivity and total biomass to UVR in the oligotrophic raw water from Lake Fuxian, but the positive responses of total biomass to UVR in the nutrient enrichment treatment. Furthermore, the response of phytoplankton to UVR was also taxa dependent. Chlorophytes and dinoflagellates showed positive response to UVR, whereas chrysophytes were quite sensitive to UVR; diatoms had no significant response to UVR under all nutrient conditions, while the response of cyanobacteria to UVR was highly dependent on nutrient status. This study highlights that the increase in nutrient concentrations in oligotrophic lake not only directly promotes the growth of phytoplankton but also combines with low UVR during summer to benefit the growth of eutrophic taxa based on the non-negative effect of UVR on total phytoplankton biomass and the positive effect on eutrophic taxa.

Particulate organic matter release below melting sea ice (Terra Nova Bay, Ross Sea, Antarctica): Possible relationships with zooplankton

Timing and rates of release of particulate organic matter (POM) beneath the Antarctic sea ice during the melting season are relatively unknown. To shed light on this topic, we investigated: i) quantity and biochemical composition of POM released below annual sea ice in Terra Nova Bay (TNB, Ross Sea, Antarctica) through sediment traps deployed at 10- and 30-m depth; ii) the abundance and taxonomic composition of phytoplankton; iii) the abundance and biochemical composition of two zooplankton species, namely the pteropods Clione limacina antarctica and Limacina helicina antarctica. Overall, our results show that in late spring-early summer in TNB the melting of annual sea ice determines a rapid release of particles into the underlying water column, and that those particles are transported downward at the rate of hours to days. POM fluxes were dominated by lipids, which probably resulted from zooplankton grazing activity on sea-ice algae and faecal pellets that were released into the water column. This, after the initial injection of particles, which were likely associated with sinking sympagic microalgal biomass derived from the sea ice melting, enhanced the nutritional value of POM. POM released beneath the sea ice, in turn, had a possible effect on the biochemical composition of the two pteropod species. Our results confirm that melting of sea ice in spring-summer each year in Antarctic coastal waters represents a fundamental step in the transfer of energy towards the higher trophic levels. Evidence of a decline in Antarctic sea ice over the last five years, plausibly as a consequence of global warming, underlines a conspicuous decline in habitat availability for sea-ice algae and, as a consequence, a drop in the availability of food for pteropods and the higher trophic levels of the coastal Antarctic Ocean.

Formation features of phytoplankton of the Bolshaya river (Omsk region) in the zoo's influence zone

According to the results of processing phytoplankton samples taken in 2018–2019 on the Bolshaya River (Omsk Region), the taxonomic composition of phytoplankton, its number and biomass were established in the zone of influence of the Bolsherechensky Zoo. As part of the phytoplankton, 183 species and intraspecific taxa from 8 divisions were identified. Seasonal dynamics of abundance of river phytoplankton and its changes in zone of zoo influence were investigated. In summer, a high level of phytoplankton development and «flowering» of water caused by Aphanizomenon flos-aquae are observed in the river on the territory of the zoo. In the formation of the number and biomass of phytoplankton, a significant share belongs to Chrysophyta and Euglenophyta. The trophic status of the Bolshaya River corresponds to the category of eutrophic waters. In autumn and summer, water in the river corresponds to the 3rd quality class of «satisfactory purity».

МЕЖГОДОВАЯ ДИНАМИКА ПЛАНКТОННЫХ СООБЩЕСТВ РУСЛОВЫХ УЧАСТКОВ КУЙБЫШЕВСКОГО ВОДОХРАНИЛИЩА

Based on the materials of hydro-biological studies in the Volga part of the Kuibyshev reservoir in 2018 and 2019, the authors evaluated changes in the quantitative indicators and taxonomic composition of phytoplankton and zooplankton. According to the results of the study, it was revealed that in 2019 the taxonomic diversity increased, but the abundance and biomass indices of phytoplankton decreased, while zooplankton decreased only in its abundance.

FEATURES OF FORMATION OF THE WINTER PLANKTON COMMUNITIES IN THE NEFTEGAVAN (“OIL HARBOUR”) - MAKHACHKALA AREA OF THE MIDDLE COASTAL CASPIAN

Made has been the analysis of the pelagic ecosystems state in the Western coastal waters of the Middle Caspian in winter period of 2020 in the Neftegavan area, Seaport of Makhachkala. The taxonomic composition of phytoplankton and zooplankton communities, and the density of hydrobionts inhabiting them have been determined. It is noted that in phytocenoses during mass blossom of Rhizosolenia calcar avis (Schultze,1843) the diatom water plants (Bacillariophyta) dominated, and in zooplankton communities the paddle-footed crustaceans, mainly acarcidis ( Acartai tonsa Dana,1843) dominated on abundance. All sampling stations were characterized by a high degree of similarity of phyto-zooplankton in taxonomic composition but they differed significantly in number and biomass.

Environmental and Biological Determinants of Algal Lipids in Western Arctic and Subarctic Seas

The Arctic is undergoing numerous environmental transformations. As a result of rising temperatures and additional freshwater inputs, ice cover is changing, with profound impacts on organisms at the base of food webs and consequently on the entire Arctic ecosystem. Indeed, phytoplankton not only provide energy as lipids, but also essential fatty acids (EFA) that animals cannot synthesize and must acquire in their diet. Omega-3 (ω3) and omega-6 (ω6) polyunsaturated fatty acids (PUFA) are essential for the healthy development and function of organisms. The high energy potential of monounsaturated fatty acids (MUFA) is of particular importance in cold waters, and various fatty acids including saturated fatty acids (SFA) are involved in organismal responses to environmental stressors. Yet relatively little is known of how variability or change in physicochemical seawater properties (e.g., temperature, light, salinity, pH and nutrients) may affect lipid synthesis in polar environments, either directly, by altering algal physiology, or indirectly, by promoting shifts in phytoplankton species composition. Here we investigated these two possibilities by sampling along a 3,000-km transect spanning 28 degrees of latitude across the subarctic and Arctic domains of Canada. The taxonomic composition of phytoplankton mainly drove the FA profiles measured in particulate organic matter (POM). Strong, positive correlations between 16:1ω7 and diatoms were observed while the proportion of PUFA and ω6 FA increased with flagellate abundance. Among specific FAs, eicosapentaenoic acid (EPA; 20:5ω3) was positively correlated with diatoms but the expected relationship between docosahexaenoic acid (DHA; 22:6ω3) and dinoflagellates was not observed. Decreasing pH had a negative effect on EPA and MUFA proportions, and DHA proportions tended to decrease with higher temperature. These two effects were primarily driven by differences in phytoplankton assemblage composition. Overall, the results of this geographically extensive study provide new information into the use of lipid markers and the ecological determinants of FA synthesis in the North. It also highlights the importance of long-lived subsurface chlorophyll maximum layers in supplying PUFA-rich POM to the food web and suggests that this situation may persist despite ongoing changes in the physical environment.

Solar radiation and solar radiation driven cycles in warming and freshwater discharge control seasonal and inter‐annual phytoplankton chlorophyll a and taxonomic composition in a high Arctic fjord (Kongsfjorden, Spitsbergen)

AbstractFjords on the west coast of Spitsbergen experience variable Arctic and Atlantic climate signals that drive seasonal and inter‐annual variability of phytoplankton productivity and composition, by mechanisms that are not fully resolved. To this end, a time series (2013–2018) of Kongsfjorden (N 78°54.2, E 11°54.0) phytoplankton pigments, ocean physics, nutrient concentrations, and microbial abundances was investigated. Kongsfjorden phytoplankton dynamics were predominantly governed by solar radiation and cycles of warming and freshwater discharge that caused pronounced changes in light and nutrient availability. Phytoplankton growth after the polar night commenced in March in a mixed, nutrient loaded water column, and accelerated in April after weak thermal stratification. Spring (weeks 10–22) showed high diatom relative abundance that ceased when silicic acid and nitrate reached limiting concentrations. Summer (weeks 23–35) was characterized by sixfold stronger stratification due to increased freshwater discharge and continued ocean heating. This caused a warm, low salinity surface layer with low nutrient concentrations. Small and diverse flagellates, together with high bacterial and viral abundances, thrived in this regenerative, N or P‐limited system. Elevated late summer chlorophyll a (Chl a), and ammonium suggested increased regeneration and nutrient pulses by glacial upwelling. Fall (weeks 36–48) caused rapidly declining Chl a and increasing diatom relative abundance, which persisted throughout the polar night, causing high diatom relative abundance during spring. Despite inter‐annual variability in ocean temperature and salinity we observed relatively stable seasonal phytoplankton taxonomic composition and Chl a.

Stable C and N Isotope Composition of Suspended Particulate Organic Matter in the Neva Estuary: The Role of Abiotic Factors, Productivity, and Phytoplankton Taxonomic Composition

Knowledge of carbon and nitrogen isotopic ratios in organic matter and their changes is important when studying nutrient cycles in aquatic ecosystems. Relationships between δ13C and δ15N values of suspended particulate organic matter (POM), water temperature, salinity, pH, redox potential, chlorophyll a concentration, primary production, and biomasses of different taxonomic groups of phytoplankton in the Neva Estuary were statistically analyzed. We tested the hypothesis that the studied physicochemical and biogeochemical characteristics, as well as the species composition of phytoplankton and its productivity, can be significant predictors of changes in the isotopic ratios of suspended particulate organic matter in estuaries. In the Neva Estuary, δ13CPOM (−16.8–−27.6‰) and δ15NPOM (2.3–7.3‰) changed synchronously. Statistical analysis showed that for both isotopes, the photosynthetic activity and taxonomic composition of phytoplankton are important. For 13CPOM, the second most important factor was water salinity, which was apparently associated with the transition of algae from CO2 to HCO3 consumption during photosynthesis in estuarine waters. For 15NPOM changes, the most important abiotic factor was pH. The study showed that the dependences of POM isotopic ratios on environmental variables obtained for continental and oceanic waters are also valid in transitional zones such as the Neva Estuary.